Most folks on the Forums assume the word "road bike" means a "pretend" racing bike...a bike that is a copy of the bikes currently used for road racing. In 2008, both real road racing bikes and pretend racing bikes use rims designed for tires with a bead seat diameter of 622. Such tires are marked as 700c plus their width.

Racing bikes prior to 1985 and touring bikes prior to 1990 usually had rims with a bead seat diameter of 630, and those tires are marked as "27" plus their width. Such tires are still made by Continental and other companies, and cheapo 27 tires are often sold at K-Mart, Wal-Mart, and Ace Hardware. In Bumbuck, Montana, it may be easier to find a size 27 tire than a 700c tire.

Many bikes are designed for riding on roads for the 99% of cyclists who do not race. Such bikes sometimes use tires with smaller bead seat diameters, because a wheel with a smaller diameter is more durable, and a smaller diameter wheel makes it easier to design a frame to fit shorter cyclists.

Some of those smaller bead seat diameters include 597 (older Schwinns), 590 (older English bikes) 559 (the mountain bike diameter now common on many hybrid road bikes) 571 (a popular French touring wheel now becoming popular again for custom touring bikes).